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Messages - Mprall00

#16
Interesting... so i bypassed all the SS by literally removing it from the chassis (unplugged the connectors for CN1a, CN2A, CN3b, and CN7a) and bolting a new input with a 1meg from input to ground just acting as a pull down resistor to the existing input hole.  Then ran that input and ground to CN3a. 

Sounds like we accomplished the same thing because i then had the input straight in to CN3b which is r13 (which I had changed it to 68k because that was what i found in other fender schematics).

But I am missing your 1meg in line before v1 right?  I don't see that in other fender schematics.  Seems very high.  Is it serving a purpose there?  Doesn't seem like it would do anything to the tone right?  68k in series with 1meg before v1...

Thanks for your help!  Learning a lot.

It sounds good without the 1meg in series, so i think I have the tube amp part solid.  Just wondering how the 1meg would effect it.
#17
Good advice.  Question:  I managed to bypass the u3a but I bypassed all of u3 so lost the boost too.  I pulled the leg of r33 and went to cn3a from that spot.  Can I keep the boost in place by starting somewhere else?  Not seeing where that would be.


#18
I went with 510k.  That with the 100k for r4 and r5 and the 250k gain pot changed the eq of the amp quite a bit.  I think i am going to up the gain pot to 500k now and thats it!  Works great with pedals.  If anything now it is too bassy and the the treble is way more tame.  I may play with values a little more but I think its a pretty happy medium now.

Here is another thing I plan on playing with - a switch to bypass the u3 solid state front end instead of using 2 inputs with a switch to select between them.  But... that will leave the buffers in place from the TS and boost so that may change the tone of having a input straight in to r13 to V1...

I'll take ideas if you have them.   :tu:
#19
Quote from: phatt on January 29, 2019, 07:35:18 AM
You could replace R72 with 560k and change your new gain pot with 250k.
Also replace R4 and R5 with 100k,, that will back off the gain.
Is R13 (56k) still in circuit?

You can alter the tone stack might help back off excess treble.
Make C23 100nF and C22 22nF might work,, not sure how well but suck it and see.
Phil.


Cool thanks.  I will try it!  r13 is still there.  I have a 510k metal film on hand to replace r72 with and a 250ka pot.  So I will probably try that as well as the 2 100k changes for r4 and r5.  i already replaced those with metal film in my quest to get the noise floor down but will sub in the 100k and see how that impacts it too.  That 50k difference in your recommendation at r72 won't impact much will it?  Slightly more gain?

I already changed the tone stack to more standard fender cap values.  C23 to 100n and C24 to 250p.  Left the mid cap alone at 47n for now.  The tone is good.  A tiny bit bright but treble knob is just running lower than normal and sounds good clean.
#20
Quote from: phatt on January 28, 2019, 01:10:32 AM
Sorry but
Unless you tell us Where Exactly in the circuit have you inserted the new input,,it's all meaningless?
could be  VR9?  or at R33?

Forget the presence idea,, bad for the PI stage. xP
Phil.

I just added an input jack with a 1meg resistor and went straight in to cn3b which eliminated the TS, boost, and solid state always on gain.  Actually took that whole input PCB out for now, which means the "effects loop" does nothing now. 

Replaced r17 with the 50k pot for gain.  It sounds good now.  Incredibly loud.  It was oddly quiet stock for 30 watts - quieter than my blues junior by a good bit.  But its not pedal friendly really now.  Thought I could tame some highs by cutting back the presence maybe?  Or maybe adding a tone control earlier between v1 and v2?

Just learning and experimenting with this one.  Will take any advice.  Thanks!
#21
Quote from: phatt on October 16, 2018, 08:31:37 AM
No way to really know without an A/B test circuit. :-\
But I'm guessing that with the Valve preamp section running wide open and then gain at 1C3A you are bound to have some hiss.

You can always reduce R4 and 5 too a more sane 100k that will reduce some excess hiss but be aware that U3A is active even when the TS part is switched out.
As far as the Valve section goes it's a Marshall/Bassman type circuit but volume is after tone stack which means the preamp is full on all the time so hiss will be evident even at lower setting of volume.
R17 could be made as a pot for preamp gain, that might have worked better.

Sorry I can't think of anything else,
Phil.

Hey.  The gain knob pointer was great.  Got it on 50k right now and seems to have good range.  I actually bypassed the entirety of the solid state front end now on a switch and it sounds way better.  Most of the noise is gone and it sounds much clearer now. 

I have another question.  Is this how I would add a presence control?  5k pot in series with a 100nf cap coming off between r25 and c16?
#22
Quote from: phatt on October 16, 2018, 08:31:37 AM
No way to really know without an A/B test circuit. :-\
But I'm guessing that with the Valve preamp section running wide open and then gain at 1C3A you are bound to have some hiss.

You can always reduce R4 and 5 too a more sane 100k that will reduce some excess hiss but be aware that U3A is active even when the TS part is switched out.
As far as the Valve section goes it's a Marshall/Bassman type circuit but volume is after tone stack which means the preamp is full on all the time so hiss will be evident even at lower setting of volume.
R17 could be made as a pot for preamp gain, that might have worked better.

Sorry I can't think of anything else,
Phil.

Awesome. Thanks for the advice!
#23
Quote from: phatt on October 13, 2018, 08:49:58 AM
I don't have that Amp but a read of the schematic tells me it will matter little as 12 volts is still within the 16 Volt cap ratings.
I doubt you would hear any difference in the sonic result.
Though V1 will last longer if heater is running 12Volts :tu:
Phil.

Thanks! Along with making v1 last longer, might it reduce the hiss? It adds white noise as I turn up the volume currently.  It seems to be coming from v1 as it disappears when I pull v1. I replaced the coupling caps and grid and plate resistors with metal film 1 watt resistors. Decreased the grid to 10k while I was at it. Reduced the hiss some but still not as quite as my tsa15... that amp has proper power to the preamp so wondering if it would help with noise too...?
#24
Reviving because I need to know - did anyone swap the regulator without changing r46? Haven't verified everything in the path is rated over 12.6v so thought i would check if anyone already did it. If so, did it change the sound?